1. Field of the Invention
The present invention relates to a microarray chip and, more particularly, to a cellular microarray which is used for cellular-adhesion via dielectrophoresis.
2. Description of Related Art
Currently, the cellular microarray has become a focus due to that it can be widely used in medical diagnosis, drug screening, and cellular research. For example, various cells can be planted to a cellular microarray, and then reagents are delivered to the cellular microarray to test the chemical interaction with these cells. Using the method illustrated above can rapidly detect the interactions between the drugs and the various cells at the same time. Hence, the cellular microarray can be employed in research and in clinical application to save time and improve the screening efficiency. However, planting cells by point to point through arrayers to manufacture the general cellular microarray is very time-consuming (about ten hours to several days) and extremely expensive. Hence, even though the cellular microarray has the potential for widely-spread application, it is difficult to employ the cellular microarray in research and clinical application at a large scale.
Many studies have indicated that cellular microarray is a convenient and efficient tool for pathological classification or drug screening. In addition, in order to upgrade the accuracy of the clinical test, screening the decease-related cells correctly is very essential for making the gene expression profile with high reliability.
In U.S. Pat. No. 6,936,151, Lock et al. have disclosed electrodes for generating and analyzing dielectrophoresis. In a method of manipulating particles suspended in a liquid medium, a moving standing wave ultrasonic vibration and an electrical field capable of generating a dielectrophoretic force on the particles are applied. The ultrasonic vibration may be applied to move the particles from a first suspending liquid to a second suspending liquid, or to move the particles into proximity with electrodes to apply the dielectrophoretic force, or to move the particles into the center of the liquid medium. Alternatively, the ultrasonic vibration and the electrical field may be applied simultaneously.
Furthermore, in U.S. Pat. No. 5,795,457, Pethig et al. have disclosed a method for manipulation of particles. By applying two or more electrical fields (DC, AC, pulsed) of different characteristics to an electrode array on e.g. the wall of a treatment cell, particles suspended in liquid in the cell may be manipulated as desired on a microscopic scale, in particular by exploiting the dielectrophoretic properties of the particles. The particles may be solid, semi-solid or liquid, and may be of simple materials or may be biological particles such as whole cells or fragments thereof.
In addition, in WO Patent No. 2007079663, Wang et al. have disclosed a methods for improving efficiency of cell electroporation using dielectrophoresis-assisted cell localization and uses thereof in a microfluidic biochip system. Cells are first subject to dielectrophoresis and localized to regions where the electric field intensity is high enough to render cells electroporated. The invention enhances the efficiency of in situ cell electroporation on a traditional microfluidic biochip.
D. R. Albrecht et al. have disclosed two independent methods for creating living cell arrays that are encapsulated within a poly(ethylene glycol)-based hydrogel to create a local 3-D microenvironment (D. R. Albrecht, et al. Lab Chip. 2005, 5, 111-118). First, “photopatterning” selectively crosslinks hydrogel microstructures containing living cells with ˜100 μm feature size. Second, “electropatterning” utilizes dielectrophoretic forces to position cells within a prepolymer solution prior to crosslinking, forming cell patterns with micron resolution. D. R. Albrecht et al. further combine these methods to obtain hierarchical control of cell positioning over length scales ranging from microns to centimeters. This level of microenvironmental control should enable the fabrication of next-generation cellular microarrays in which robust 3-D cultures of cells are presented with appropriate physical and chemical cues and, consequently, report on cellular responses that resemble in vivo behavior.
Further, D. R. Albrecht et al. have provided a method for the rapid formation of reproducible, high-resolution 3D cellular structures within a photopolymerizable hydrogel using dielectrophoretic forces (D. R. Albrecht, et al. Nat Methods. 2006, 3, 369-375). It shows that the parallel formation of >20,000 cell clusters of precise size and shape within a thin 2-cm2 hydrogel and the maintenance of high cell viability and differentiated cell markers over 2 weeks. By modulating cell-cell interactions in 3D clusters, the results show that microscale tissue organization regulates bovine articular chondrocyte biosynthesis. Hence, this platform permits investigation of tissue architecture in other multicellular processes, from embryogenesis to regeneration to tumorigenesis.
Besides, D. R. Albrecht et al. have also provide a method to form multiphase tissues consisting of microscale tissue sub-units in a “local phase” biomaterial, which are organized by dielectrophoresis (DEP) forces in a separate, mechanically supportive “bulk phase” material (D. R. Albrecht, et al. Lab Chip. 2007, 7, 702-709). First, D. R. Albrecht et al. define the effects of medium conductivity on the speed and quality of DEP cell patterning. Then, D. R. Albrecht et al. produce multiphase tissues with microscale architecture that combine high local hydrogel conductivity for enhanced survival of sensitive liver progenitor cells with low bulk conductivity required for efficient DEP micropatterning. This approach enables an expanded range of studies examining the influence of 3D cellular architecture on diverse cell types, and in the future may improve the biological function of inhomogeneous tissues assembled from a variety of modular tissue sub-units.
Y. Huang et al. disclosed a microelectronic chip array on a silicon wafer fabricated by semiconductor manufacturing process. The disclosed microelectronic chip array includes plate-electrodes, and agarose covered thereon and functions as a cell adhesion layer. Since different cells have different dielectrophoresis properties, this microelectronic chip array is capable of separating various cells by adjusting the voltage (Y. Huang, et al. Anal. Chem. 2002, 74, 3362-3371).
The purpose of Y. Huang et al. is to screen a specific cell type in heterogeneous cells. Therefore, it is possible to screen a specific cell type from heterogeneous cells successfully and to generate the gene expression profile of the specific cell type correctly by using the plate-electrodes. However, the disadvantage of the plate-electrodes is that the distribution of the cells on the electrodes is not uniform, and parts of the electrodes are not adhered with cells.
In addition, C. T. Ho et al. has disclosed a cell-patterning chip, which was manufactured by a microfabrication process. On the cell-patterning chip, many concentric electrodes were formed to mimic the lobular morphology of real liver tissue (C. T. Ho, et al. Lab Chip. 2006, 6, 724-734). The applied cell adhesion layer of the cell-patterning chip is poly-D-lysine. Furthermore, many anodes and cathodes were arranged in parallel on the cell-patterning chip to form the concentric electrodes. When ac voltage was applied, the dielectrophoresis force was formed within the cells in the electric field, and the cells were able to distribute on all electrodes of the concentric electrodes. Hence, the cell-patterning chip was able to mimic the lobular morphology of real liver tissue artificially. However, in the process of manufacturing the concentric electrodes, it took at least 12 hours to rinse the flow paths. In this way, it is possible to cover poly-D-lysine on the surface of the concentric electrodes completely. Using the cell-patterning chip illustrated above, the result of cell survival rate test showed that most of the cells were still alive on the electrodes after 1 hour.
Therefore, it is desirable to provide a cellular microarray to overcome the disadvantages illustrated above. Particularly, a cellular microarray, where the cells can be patterned with good uniformity rapidly, is needed. In addition, the cost for manufacturing and using the cellular microarray must be reduced, so that it is possible to apply the cellular microarray in research and clinical application widely.